1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a device and method for transporting printed products.
2. Background Information
U.S. Pat. No. 5,447,302 purports to disclose an apparatus for removing paper products from a stack on a hopper. The apparatus has a rotatably mounted gripper drum which rotates about a central axis at a constant angular velocity. A stationary cam is rigidly mounted adjacent the gripper drum. A cam follower follows the outer side of the cam, and is attached at one end to a link, which also rotates with the gripper drum. The rotating link is pivotable about a pin, so that a variation in the cam radius can cause the link to pivot, so that an other end of the link compresses or stretches a spring. This other end of the link connects to a further link which can retract a toggle arm on which a gripper and a gripper seat are supported. If the toggle arm is pulled so that the gripper and the gripper seat accelerate in the same direction as the movement of the gripper drum, the gripper is opened. If the gripper and the gripper seat are slowed down relative to the gripper drum, the gripper is closed.
The device of the '302 patent has the disadvantage that the link structure is complicated, especially in that a spring is required to force the cam to follow the cam follower. The repeated compression and expansion of the spring can lead to a weakening of the spring over many rotations and can cause the entire apparatus to malfunction. At high speeds, high spring forces must be maintained to keep the cam follower on the cam and the gripper from engaging properly. Departure of the follower from the cam can cause gripper malfunction or damage.
Moreover, the gripper force remains relatively constant regardless of toggle arm displacement. A large gripping force thus is necessary for thick products, which can then damage thin products if they are used on the same machine.